Suppository bases are classified into fatty bases and water-soluble bases. Although they are both excellent bases, the fatty bases have been widely employed, since they are superior to the water-soluble ones in less irritation to the administration sites, etc. It has been a practice to design suppositories containing fatty bases to melt at the body temperature. When inserted into a body cavity, therefore, such a suppository would migrate upward from the administration site.
In the case of antihemorrhoidal suppository, drugs should be retained around the affected part. Accordingly, there have been reported a number of compositions for suppositories for preventing drugs from spreading over the rectum by, for example, JP-A-54-26325, JP-A-6-40889, JP-A-63-280016, JP-A-1-143825, JP-A-61-109710, JP-A-2-15024, JP-A-4-164023 and EP No. 103995 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
However, there has been reported no suppository which sustains a melting point higher than the body temperature and thus never melts during storage but, when inserted into a body cavity, melts or gels at the body temperature owing to a decrease in its melting point.